One issue with that is if you wanted to play with your friend(s) who are a bit higher level you would be screwed. Yeah the level penalty already drops the exp, but you can at least still NM train with friends who are higher level and still get decent NM exp. Sounds good on paper but once the levels get really top heavy new players will just be alone in their own instance with barely enough players to form a train and potentially not enough roles to form a decent job comp to 8 man farm mobs. Higher level players can also more easily navigate the map and raise you if you die.
